The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Wireless networks comprising wireless sensor and/or actuator devices may be applied in many fields, e.g. seismic-sensor networks used for geological exploration, heat or smoke detectors used in fire protection, or networks with sensors or actuators for monitoring or controlling devices such as traffic lights or the like. In these applications the layout of the wireless nodes, which are usually referred to as sensor nodes, is static in the sense that a position of a node does not change once it is part of the network.
Traditional protocols for wireless networks typically involve a type of point-to-point communications, which has the disadvantage that the message may not reach its destination when a node or link in the path is not reachable. This is why currently mesh networks are developed in which all routers communicate directly with each other. In such networks nodes or access points are allowed to communicate with other nodes without being routed through a central switch point thereby eliminating centralized failure. Currently ZigBee is a popular low-power short-range wireless radio communication standard IEEE 802.15.4 for use in such mesh network. A signal may “multi-hop” among its different nodes in order to circumvent obstructions as it seeks and ultimately finds its target node. These redundant communication paths provide a reliable route for communication.
Typically, data transmission through such networks is based on routing tables, which may be either established proactively (as known from the Destination Sequence Vector Routing scheme (DSVD)), reactive (such as the Ad-hoc On Demand Vector scheme (AODV)) or a combination thereof (e.g. the hybrid wireless mesh protocol (HWMP) as defined in IEEE 802.11s). The routing tables are typically established during a “route discovery and maintenance mode” of operation. A routing scheme based on routing tables has the disadvantage that the tables need to be updated every time changes are made in the network. Especially in large networks comprising e.g. a thousand nodes these routing updates may introduce sizable overhead.
The article of Mauve et al. “A survey on position-based routing in mobile ad hoc networks,” Network, IEEE, vol. 15, no. 6, pp. 30-39, November/December 2001 describes position-based protocols for mobile ad-hoc networks that do not use routing tables for data transmission to a particular point in a mesh network. In such protocols a message comprises a destination and the nodes know the positions of their neighbors, which are constantly updated using a location service. An algorithm may be used to estimate which forward node is best suited for transporting data to a predetermined destination. Although no routing tables are used, these protocols require a location service that introduces a large overhead. This routing scheme however has the problem that when a package is sent forward to a node closer to the destination, it may get stuck in a local minimum wherein the receiving node cannot find a node closer to the destination than itself. This type of errors may compromise the reliability of the network.
A further problem is that a position-based protocol should not only provide highly reliable data transfer but should also enable low power data transmission and/or optimized performance with respect to other network and/or node parameters such as: equalization of power consumption in all or a predetermined part of the nodes in the mesh network; minimum (average) power consumption; minimum transport time for data acquisition at a sensor node to reception of the data at a data sink; maximum data throughput through the mesh network; minimum number of collisions or no collisions at all; constraints on the TDMA schedule for time slot allocation; degree of fault tolerance, etc.
Hence, from the above it follows that there is a need in the art for improved protocols, in particular position-based broadcast protocols, for use in a wireless mesh network and wireless (sensor) devices that are configured using such improved position-based broadcast protocol.